As is known, glass sheets and the like are currently worked by using conveyance assemblies designed to feed the sheet below the working heads, which perform the required work.
According to the background art, the conveyance assembly is provided with presser rollers or belts, which engage the surface of the sheet and retain it during work; these means very often cause damage to the surface of the sheet, especially when working on glass sheets with a “LOW-E” type coating.
In order to try to solve this problem, solutions have already been introduced in which the conveyance assembly is provided by means of two pairs of belts arranged on opposite sides along the sheet advancement direction and retain the sheet only upstream of the work area.
One of such sides is typically fixed, while the other pair of belts can perform a translational motion so as to adapt easily to the width of the sheet.
Each pair of belts is formed by a belt which is fixed on the supporting surface and engages the lower side of the sheet, while the other belt can move vertically in order to engage the upper side so as to apply an adequate pressure which ensures the retention of the sheet during work.
With this type of conveyance assembly, it is possible to perform work only along the sides affected by the belts and with a single direction of advancement.
Another problem consists further in that it is not always possible to retain the sheet firmly, and therefore work imperfections and vibrations can occur which damage the tools and produce lower-quality work.